Critical Fix:
The previous implementation incorrectly calculated scale factors because
calculate_page_dimensions() was prioritizing source file dimensions over
OCR coordinate analysis, resulting in scale=1.0 when it should have been ~0.27.
Root Cause:
- PaddleOCR processes PDFs at high resolution (e.g., 2185x3500 pixels)
- OCR bbox coordinates are in this high-res space
- calculate_page_dimensions() was returning source PDF size (595x842) instead
- This caused scale_w=1.0, scale_h=1.0, placing all text out of bounds
Solution:
1. Rewrite calculate_page_dimensions() to:
- Accept full ocr_data instead of just text_regions
- Process both text_regions AND layout elements
- Handle polygon bbox format [[x,y], ...] correctly
- Infer OCR dimensions from max bbox coordinates FIRST
- Only fallback to source file dimensions if inference fails
2. Separate OCR dimensions from target PDF dimensions:
- ocr_width/height: Inferred from bbox (e.g., 2185x3280)
- target_width/height: From source file (e.g., 595x842)
- scale_w = target_width / ocr_width (e.g., 0.272)
- scale_h = target_height / ocr_height (e.g., 0.257)
3. Add PyPDF2 support:
- Extract dimensions from source PDF files
- Required for getting target PDF size
Changes:
- backend/app/services/pdf_generator_service.py:
- Fix calculate_page_dimensions() to infer from bbox first
- Add PyPDF2 support in get_original_page_size()
- Simplify scaling logic (removed ocr_dimensions dependency)
- Update all drawing calls to use target_height instead of page_height
- requirements.txt:
- Add PyPDF2>=3.0.0 for PDF dimension extraction
- backend/test_bbox_scaling.py:
- Add comprehensive test for high-res OCR → A4 PDF scenario
- Validates proper scale factor calculation (0.272 x 0.257)
Test Results:
✓ OCR dimensions correctly inferred: 2185.0 x 3280.0
✓ Target PDF dimensions extracted: 595.3 x 841.9
✓ Scale factors correct: X=0.272, Y=0.257
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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